Scientists have discovered that a strain of Ebola virus isolated from wild apes in the Gabon/Congo region belongs to a new lineage and is capable of genetically merging with other strains of the virus to create new variants.

This ability of the lethal virus to 'recombine' genetic material has important implications for vaccine development, write the researchers. A vaccine that is made up of weakened viruses could merge with the wild virus to form new strains, making the spread of the virus in humans and apes harder to predict and control.

The findings were published online this week (17 October) in the Proceedings of the National Academy of Sciences.

Scientists from the International Centre for Medical Research in Franceville, Gabon, and their colleagues genetically analysed samples of Zaire Ebola virus — the most virulent type, which causes haemorrhagic fever and death within days in almost 90 per cent of infected people — taken from carcasses of great apes.

They identified a new strain, strain B, that is genetically different from the strain A samples collected in past outbreaks from infected humans.

The researchers estimate that strain B probably evolved just before the first recorded human outbreak in 1976. They confirmed that it was the cause of outbreaks in humans in the Republic of Congo in 2003 and 2005.

This discovery indicates that outbreaks in humans could be caused not just by strain A, which is spreading through central Africa, but also by multiple emerging viruses.

There is evidence that the A and B strains may have recently recombined — probably when both were present in the same host — to form a group of recombinant viruses that triggered outbreaks in 2001–03.

The researchers hope that their findings will help to develop better methods for predicting and controlling outbreaks.

But we still need to know more about how human outbreaks occur, study author Jean-Paul Gonzales, from the Research Institute for Development at Mahidol University in Thailand, told SciDev.Net. For example, we need to know whether recombinant strains are the main source of infection and more about the role of bats as a viral reservoir.